So regarding Maggy's prophecy about Cersei...
Okay, I know we're talking about a fictional universe, but I'm still going to get technical.
When it comes to GOT (or ASOIAF), the storyline is influenced by actual historical events (magic and dragons aside). Therefore, I like to think that prophecy is 100% subjective, open to interpretation, and guided to fruition by the influence of men (as opposed to divine intervention or inescapable fate). What I'm trying to say is that prophecies are poppycock, even in GOT. The characters in this story interpret information retrospectively and find ways to make current day events meet the criteria for the prophecies that exist in within their cultures.
Characters like Cersei (or even Dany) often allow or readily work towards the fulfillment of their own personal prophecies, even when the prospective outcome is tragic. Cersei's children didn't all
have to die. She could have left King's Landing and took them back to Casterly Rock to live out their lives way back in season 1. She could have
not blown up Tommen's wife, thereby prompting him to end his own life. Dany could have remained in Essos and carried on as a successful liberator and ruler and two of her dragons might not be dead now, but her vision in the House of the Undying dangled the Iron Throne under her nose.
I think Cersei's fourth pregnancy has opened her eyes to the fact that prophecies aren't set in stone and that you establish your own destiny. I think Cersei isn't going to let the remainder of Maggy's prophecy come to pass. Dany, on the other hand, I think she's going to die in pursuit of the prophecy that led her back to Westeros...?